cmd: remove some unnecessary gotos

Pick the low-hanging fruit, which are the gotos that don't go very far
and labels that aren't used often. All of them have easy replacements
with breaks and returns.

One slightly tricky rewrite is defaultlitreuse. We cannot use a defer
func to reset lineno, because one of its return paths does not reset
lineno, and thus broke toolstash -cmp.

Passes toolstash -cmp on std cmd.

Change-Id: Id1c0967868d69bb073addc7c5c3017ca91ff966f
Reviewed-on: https://go-review.googlesource.com/110063
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/const.go

@@ -1344,6 +1344,8 @@ func defaultlitreuse(n *Node, t *types.Type, reuse canReuseNode) *Node {
 		default:
 			yyerror("defaultlit: unknown literal: %v", n)
 		}
+		lineno = lno
+		return n
 
 	case CTxxx:
 		Fatalf("defaultlit: idealkind is CTxxx: %+v", n)
@@ -1354,28 +1356,19 @@ func defaultlitreuse(n *Node, t *types.Type, reuse canReuseNode) *Node {
 			t1 = t
 		}
 		n = convlit1(n, t1, false, reuse)
-
-	case CTINT:
-		t1 = types.Types[TINT]
-		goto num
-
-	case CTRUNE:
-		t1 = types.Runetype
-		goto num
-
-	case CTFLT:
-		t1 = types.Types[TFLOAT64]
-		goto num
-
-	case CTCPLX:
-		t1 = types.Types[TCOMPLEX128]
-		goto num
-	}
-
 		lineno = lno
 		return n
 
-num:
+	case CTINT:
+		t1 = types.Types[TINT]
+	case CTRUNE:
+		t1 = types.Runetype
+	case CTFLT:
+		t1 = types.Types[TFLOAT64]
+	case CTCPLX:
+		t1 = types.Types[TCOMPLEX128]
+	}
+
 	// Note: n.Val().Ctype() can be CTxxx (not a constant) here
 	// in the case of an untyped non-constant value, like 1<<i.
 	v1 := n.Val()

src/cmd/compile/internal/gc/walk.go

@@ -1008,7 +1008,8 @@ opswitch:
 	case OCONV, OCONVNOP:
 		if thearch.SoftFloat {
 			// For the soft-float case, ssa.go handles these conversions.
-			goto oconv_walkexpr
+			n.Left = walkexpr(n.Left, init)
+			break
 		}
 		switch thearch.LinkArch.Family {
 		case sys.ARM, sys.MIPS:
@@ -1062,8 +1063,6 @@ opswitch:
 				}
 			}
 		}
-
-	oconv_walkexpr:
 		n.Left = walkexpr(n.Left, init)
 
 	case OANDNOT:

src/cmd/internal/obj/arm64/asm7.go

@@ -1470,7 +1470,7 @@ func (c *ctxt7) aclass(a *obj.Addr) int {
 		case obj.NAME_NONE:
 			c.instoffset = a.Offset
 			if a.Reg != 0 && a.Reg != REGZERO {
-				goto aconsize
+				break
 			}
 			v := c.instoffset
 			if v == 0 {
@@ -1516,7 +1516,7 @@ func (c *ctxt7) aclass(a *obj.Addr) int {
 
 		case obj.NAME_EXTERN, obj.NAME_STATIC:
 			if a.Sym == nil {
-				break
+				return C_GOK
 			}
 			if a.Sym.Type == objabi.STLSBSS {
 				c.ctxt.Diag("taking address of TLS variable is not supported")
@@ -1531,7 +1531,6 @@ func (c *ctxt7) aclass(a *obj.Addr) int {
 				a.Reg = obj.REG_NONE
 			}
 			c.instoffset = int64(c.autosize) + a.Offset
-			goto aconsize
 
 		case obj.NAME_PARAM:
 			if a.Reg == REGSP {
@@ -1540,11 +1539,10 @@ func (c *ctxt7) aclass(a *obj.Addr) int {
 				a.Reg = obj.REG_NONE
 			}
 			c.instoffset = int64(c.autosize) + a.Offset + 8
-			goto aconsize
+		default:
-		}
 			return C_GOK
+		}
 
-	aconsize:
 		if isaddcon(c.instoffset) {
 			return C_AACON
 		}

src/cmd/internal/obj/mips/asm0.go

@@ -612,13 +612,11 @@ func (c *ctxt0) aclass(a *obj.Addr) int {
 				return C_DACON
 			}
 
-			goto consize
-
 		case obj.NAME_EXTERN,
 			obj.NAME_STATIC:
 			s := a.Sym
 			if s == nil {
-				break
+				return C_GOK
 			}
 
 			c.instoffset = a.Offset
@@ -650,11 +648,11 @@ func (c *ctxt0) aclass(a *obj.Addr) int {
 				return C_SACON
 			}
 			return C_LACON
+
+		default:
+			return C_GOK
 		}
 
-		return C_GOK
-
-	consize:
 		if c.instoffset >= 0 {
 			if c.instoffset == 0 {
 				return C_ZCON

src/cmd/internal/obj/mips/obj0.go

@@ -878,21 +878,20 @@ func (c *ctxt0) sched(p0, pe *obj.Prog) {
 			t = sch[j:]
 			if t[0].comp {
 				if s[0].p.Mark&BRANCH != 0 {
-					goto no2
+					continue
 				}
 			}
 			if t[0].p.Mark&DELAY != 0 {
 				if -cap(s) >= -cap(se) || conflict(&t[0], &s[1]) {
-					goto no2
+					continue
 				}
 			}
 			for u := t[1:]; -cap(u) <= -cap(s); u = u[1:] {
 				if c.depend(&u[0], &t[0]) {
-					goto no2
+					continue
 				}
 			}
 			goto out2
-		no2:
 		}
 
 		if s[0].p.Mark&BRANCH != 0 {

src/cmd/internal/obj/ppc64/asm9.go

@@ -844,13 +844,11 @@ func (c *ctxt9) aclass(a *obj.Addr) int {
 				return C_DACON
 			}
 
-			goto consize
-
 		case obj.NAME_EXTERN,
 			obj.NAME_STATIC:
 			s := a.Sym
 			if s == nil {
-				break
+				return C_GOK
 			}
 
 			c.instoffset = a.Offset
@@ -871,11 +869,11 @@ func (c *ctxt9) aclass(a *obj.Addr) int {
 				return C_SACON
 			}
 			return C_LACON
+
+		default:
+			return C_GOK
 		}
 
-		return C_GOK
-
-	consize:
 		if c.instoffset >= 0 {
 			if c.instoffset == 0 {
 				return C_ZCON

src/cmd/internal/obj/s390x/asmz.go

@@ -570,13 +570,12 @@ func (c *ctxtz) aclass(a *obj.Addr) int {
 				}
 				return C_DACON
 			}
-			goto consize
 
 		case obj.NAME_EXTERN,
 			obj.NAME_STATIC:
 			s := a.Sym
 			if s == nil {
-				break
+				return C_GOK
 			}
 			c.instoffset = a.Offset
 
@@ -605,11 +604,11 @@ func (c *ctxtz) aclass(a *obj.Addr) int {
 				return C_SACON
 			}
 			return C_LACON
+
+		default:
+			return C_GOK
 		}
 
-		return C_GOK
-
-	consize:
 		if c.instoffset == 0 {
 			return C_ZCON
 		}